Wireless terminal methods and apparatus for use in a wireless communications system that uses a multi-mode base station

ABSTRACT

Wireless terminal for use with a multi-mode base station that supports a transmit standby mode and an active mode is described. Transmit standby mode of base station operation is a low power/low interference level of operation as compared to active mode. In transmit standby mode at least some of the synchronization signaling such as pilot tone signaling is reduced in power level and/or rate with respect to the active mode. In transmit standby mode, the base station has no active state registered wireless terminals being serviced but may have some sleep state registered wireless terminals being serviced. Mode transitions from active to transmit standby may be in response to: a detected period of inactivity, scheduling information, base station mode change signals, and/or detected wireless terminal state transition. Mode transitions from transmit standby to active may be in response to: scheduling information, access signals, wake-up signals from the wireless terminal, hand-off signals, etc.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for implementingwireless communications systems where the apparatus may include, forexample, base stations which support multiple modes of operation and/orwireless terminals for interacting with base stations which supportmultiple modes of operation.

BACKGROUND OF THE INVENTION

Typically, in a wireless communications system, the base stations arepowered on and continuously operated in an active mode of operation. Inthis active mode of operation, the base station is operated inaccordance with a downlink timing and frequency structure, e.g., arepetitive timing and frequency structure. Synchronization signals, suchas beacon signals and pilot signals, are transmitted on a scheduledbasis at associated predetermined power levels. The power levels andrate of transmission of these synchronization signals do not typicallyvary regardless of the number and/or state of users being currentlyserviced by the base station. In high population density cellularcoverage areas, this in not a significant consideration, as there isusually at least one or more active users at any given time using thebase station as their network point of attachment and communicating userdata. Those active wireless terminals need the full level ofsynchronization signals such as to maintain precise timingsynchronization and maintain accurate current channel estimates.

However, in some cellular coverage areas, such as remote rural areashaving low population densities and/or areas having widely varying loadrequirements as a function of time or a schedule, it would beadvantageous if methods and apparatus were developed which allowed abase station to be operated, at certain time and/or under certainconditions, such as to reduce transmission power and/or reduceinterference generated by the base station. For example, consider that abase station, e.g., a base station along a train track in a rural area,may have significant time intervals where the base station does not haveany registered wireless terminals that need to communicate user data,e.g., receive and/or transmit user data. Under such a situation, duringsuch a time interval the base station power is wasted by transmittingthe full set of synchronization signals at the normal power levels. Inaddition, neighboring cells, which may have high population densitiesand typically have many active users, will be adversely affected by theinterference generated from the unnecessary synchronization broadcastsignaling. By reducing the interference level experienced in an adjacentcell the data throughput in that adjacent cell can be increased, e.g.,by being able to increase the coding rate for a given transmission powerlevel and modulation scheme.

It would be desirable if methods and apparatus were developed whichallowed for reducing broadcast synchronization signals in response tochanging system conditions. It would be beneficial if such methods andapparatus supported at least some of: rapid transitioning back to a fulllevel of synchronization signals when required, easily detectablereactivation signaling, seamless hand-off operations, and the capabilityto transition between different levels of synchronization signaling as afunction of schedule information. It would also be advantageous if themethods and apparatus developed to support multiple levels ofsynchronization signaling would still be capable of supportingregistered wireless terminals in a wireless terminal sleep stateirrespective of the level of synchronization signaling. In addition, itwould be beneficial if the low level of synchronization signaling stillprovided a wireless terminal with the capability to be able to detectthe presence of a base station and/or compare the base station'sreceived signal strength with other adjacent base stations which couldpotentially be used as network attachment points.

In view of the above, there is a need for new methods and apparatus toimplement and support multi-mode base station operations.

SUMMARY

The present invention relates to methods and apparatus for implementingwireless communications systems where the apparatus may include, forexample, base stations which support multiple modes of operation and/orwireless terminals for interacting with base stations which supportmultiple modes of operation.

Various methods and apparatus of the invention are directed to wirelessterminals that are intended for use with a base station that supportsmultiple modes of operation, e.g., a first mode such as a full-on mode,and a second mode such as a sleep mode. More than two modes of operationmay be, and in some embodiments are, supported by the base station witheach mode corresponding to, e.g., different signaling rates of at leastone periodic signal and/or different power levels used to transmit someparticular periodic signals such as a group of pilot tones or beaconsignals.

By supporting multiple modes of operation, base station transmissions ofcontrol signals can be reduced when the higher level of signaling is notrequired, e.g., when there are no active wireless terminals in the cell.By reducing base station transmissions in terms of frequency and/orpower level, interference with communications in neighboring cells canbe reduced. This allows for improved throughput in a multi-base stationsystem where transmissions by adjoining base stations can interfere withone another. Depending on the particular mode of operation, the basestation may support downlink signaling, e.g., broadcast transmission ofdata but not uplink transmissions of data which may require a higherlevel of control signaling. Modes which support both downlink and uplinkcommunication of user data, e.g., text data, image data, audio dataand/or user application data, between wireless terminals and a basestation normally correspond to one or more higher, e.g., full-on, modesof base station operation.

During different modes of base station operation, different levelsand/or rates of signaling and/or transmission output power are supporteddepending on the mode of operation. For example, in some embodiments,pilot signals and/or various control signals which are normallytransmitted at a first periodic rate in a fully on state are transmittedat a reduced rate during a sleep mode of base station operation ascompared to a full-on mode of base station operation. In someembodiments the number of pilot signals transmitted during a sleep modeis reduced during individual symbol transmission time periods during thesleep mode of operation as compared to the full-on mode of operation. Insome embodiments, the number of individual symbol transmission timeperiods during which pilot signals are transmitted during the sleep modeof operation is reduced from the number of individual symboltransmission time periods during which pilot signals are transmitted inthe full-on mode of operation, with respect to the same number of OFDMsymbol transmission time periods, e.g., the same number of successiveOFDM symbol transmission time periods representing a grouping in arepetitive downlink timing structure. In some embodiments, during apartial on or sleep mode of operation the power level at whichparticular signals are transmitted is reduced as compared to the powerlevel used during the full-on mode of operation.

Base station transition between modes of operation can be triggered in aplurality of ways. The base station may operate in different modesaccording to a predetermined schedule, e.g., a train schedule, commuterschedule or other type of schedule. Such a schedule may be designed sothat the base station will operate in the full-on state at particularpoints in time known to normally correspond to periods of wirelessterminal data communications activity. Alternatively, or in addition toscheduled modes of base station operation, in some embodiments basestations monitor for wireless terminal activity in the cell which theyserve and adjust the mode of operation to correspond to the detectedlevel of communications data activity. For example, a base station maytransition from a full-on state to a lower activity mode of operationwith less control signaling in response to detecting a period in whichno user data, e.g., text, voice or other types of user application data,have been transmitted for a predetermined period of time or when thereis a determination that the cell does not include any active orregistered wireless terminals.

Transitions from a base station sleep mode of operation to a full-onmode of operation are triggered, in some embodiments, by the receipt ofa wake up signal from a mobile node. Wireless terminal registrationsignals and/or mobile node requests to transition from a sleep mode ofmobile node operation to an active mode of mobile node operation inwhich the mobile node can transmit user data in an uplink can serve aswakeup signals and/or control signals which are used to trigger a changein base station operation from a less active to more active mode of basestation operation.

The methods and apparatus of the present invention enable wirelessterminals to interact with base stations which support different modesof activity. While transmission power conservation at the base stationsis one benefit of supporting multiple base station modes of operation,the reduced level of signal interference achieved by supporting reducedactivity modes of base station operation can increase overall systemthroughput by decreasing interference in neighboring cells whenoperating in a sleep state or other reduced activity mode of basestation operation.

Numerous additional features benefits and embodiments of the presentinvention are discussed in the detailed description which follows.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a drawing of an exemplary communications system implemented inaccordance with the present invention and using methods of the presentinvention.

FIG. 2 is a drawing of an exemplary base station, implemented inaccordance with the present invention and using methods of the presentinvention.

FIG. 3 is a drawing of an exemplary wireless terminal implemented inaccordance with the present invention and using methods of the presentinvention.

FIG. 4 is a drawing of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the active mode.

FIG. 5 is a drawing of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the transmit standby mode, for an exemplaryembodiment.

FIG. 6 is a drawing of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the transmit standby mode, for anotherexemplary embodiment.

FIG. 7 is a drawing of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the transmit standby mode, for stillanother exemplary embodiment.

FIG. 8 is a drawing illustrating an exemplary base station, implementedin accordance with the present invention, currently in an active mode ofbase station operation, wherein the base station' cell includes activewireless terminals.

FIG. 9 is a drawing illustrating an exemplary base station, implementedin accordance with the present invention, currently operating in thetransmit standby mode of operation, wherein the base station's cellincludes wireless terminals that are turned off, but does not includeany wireless terminals in the sleep state or active state.

FIG. 10 is a drawing illustrating an exemplary base station, implementedin accordance with the present invention, currently operating in thetransmit standby mode of operation, wherein the base station's cellincludes a wireless terminal that is turned off and a wireless terminalthat is in the sleep state, but does not include any wireless terminalsin the active state.

FIG. 11 is a drawing of a table illustrating characteristics of the basestation active mode of operation and the base station transmit standbymode of operation for an exemplary embodiment, in accordance with thepresent invention.

FIG. 12 is a drawing illustrating an exemplary communications systemincluding a train routed through wireless cells and schedule informationused in base station operational mode switching, the communicationsystem implemented in accordance with the present invention and usingmethods of the present invention.

FIG. 13 comprising the combination of FIG. 13A, FIG. 13B, and FIG. 13Cis a flowchart of an exemplary method of operating a base station inaccordance with the present invention.

FIG. 14 is a drawing of a state diagram for an exemplary base stationimplemented in accordance with the present invention.

FIG. 15 is a drawing of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the transmit standby mode, for stillanother exemplary embodiment.

FIG. 16 is a drawing illustrating a series of time sequential operationsin an exemplary embodiment of the present invention, the operationsincluding base station wake-up signaling communicated over a wirelesslink.

FIG. 17 is a drawing illustrating a portion of an exemplary OFDM uplinktiming and frequency structure for the purpose of explaining exemplarybase station wake-up signaling in accordance with various embodiments ofthe present invention.

FIG. 18 is a drawing illustrating exemplary access interval uplink airlink resources, exemplary segments and exemplary signaling correspondingto a base station active mode of operation and a base station transmitstandby mode of operation, in accordance with some embodiments of thepresent invention.

FIG. 19 is a flowchart of an exemplary method of operating a wirelessterminal in accordance with the present invention.

DETAILED DESCRIPTION

FIG. 1 is a drawing of an exemplary communications system 100implemented in accordance with the present invention and using methodsof the present invention. Exemplary communications system 100 may be,e.g., an orthogonal frequency division multiplexing (OFDM) multipleaccess wireless communications system. Exemplary system 100 includes aplurality of base stations (BS 1 106, BS M 108), each BS (106, 108)having a corresponding cellular coverage area (cell 1 102, cell M 104).The BSs (106, 108) are implemented in accordance with the presentinvention, and support (i) an active mode of operation and (ii) atransmit standby mode of operation. The BSs are coupled together via abackhaul network. System 100 also includes network node 110, e.g., arouter. Network node 110 is coupled to (BS 1 106, BS M 108) via networklinks (120, 122), respectively. Network link 124 couples network node110 to other network nodes, e.g., other BSs, routers,Authentication-Authorization-Accounting (AAA) nodes, home agent nodes,etc., and/or the Internet. Network links (120, 122, 124), may be, e.g.,fiber optic links, cable links, and/or high capacity radio links such asdirected microwave links.

System 100 also includes a plurality of wireless terminals (WT 1 112, WTN 114, WT 1′ 116, WT N′ 118). At least some of the WTs (112, 114, 116,118), are mobile nodes, which may move throughout the communicationssystem and establish a network point of attachment via the base stationin the cell in which it is currently located. The WTs (112, 114, 116,118) may be, e.g., cell phones, mobile data terminals, personal digitalassistants (PDAs), laptop computers, and/or other wirelesscommunications devices supporting the communication of voice, video,text, messages, and/or files. The WTs (112, 114, 116, 118), areimplemented in accordance with the present invention, to supportwireless communications signaling with the multi-mode base stations(106, 108).

WTs (112, 114) are currently situated in cell 1 102 and can be coupledto BS 1 106 via wireless links (126, 128), respectively. WTs (116, 118)are currently situated in cell M 104 and can be coupled to BS M 108 viawireless links (130, 132), respectively. WTs (112, 114, 116, 118) mayoperate in different states, e.g., an active state or a sleep state. Insome embodiments, the active state of a WT may be further qualified withthe WT supporting an active-On state and an active-Hold state.

FIG. 2 is a drawing of an exemplary base station 200, implemented inaccordance with the present invention and using methods of the presentinvention. Exemplary BS 200 may be any of the BSs (106, 108) of thesystem 100 of FIG. 1. Exemplary BS 200 includes a receiver 202, atransmitter 204, a processor 206, an I/O interface 208, and a memory 210coupled together via a bus 212 over which the various elements mayinterchange data and information. Receiver 202 is coupled to a receiveantenna 203 through which the base station 200 may received uplinksignals from a plurality of wireless terminals. Received uplink signalsmay include, e.g., access signals, base station wake-up signals, handoffsignals, WT state change signals, requests for resources, user data,power control information signals, timing control information signals,acknowledgement signals. Receiver 202 includes a decoder 214 fordecoding received uplink signals, which have been previously encoded bya WT prior to transmission, e.g., decoding a coded block of user datacommunicated in an uplink traffic channel segment. Transmitter 204 iscoupled to transmit antenna 205 via which the BS can transmit downlinksignals to WTs. Downlink signals may include, e.g., beacon signals,pilot signals, power control signals, timing control signals,registration signals, paging signals, assignment signals, and user datasignals. Transmitter 204 includes an encoder 216 for encoding downlinkdata/information, e.g., encoding a block of user data into a downlinktraffic channel segment. In different modes of base station operationdifferent sets of downlink signals may be communicated, different powerlevels may be used for the same type of downlink signal, and/or thefrequency of transmission of different signals may be different. I/Ointerface 208 provides BS 200 with an interface to the backhaul networkcoupling BS 200 to other network nodes and/or the Internet. Signalscommunicated over the I/O interface 208 may include, e.g., schedulinginformation pertaining to switching the mode of operation of BS 200, BSwake-up signals, commanded BS mode change signals, and WT handoffsignals.

Memory 210 includes routines 218 and data/information 220. The processor206, e.g., a CPU, executes the routines 218 and uses thedata/information 220 in memory 210 to control the operation of the basestation 200 and implement the methods of the present invention. Routines218 include communications routines 222 and base station controlroutines 224. Communications routines 222 implement the variouscommunications protocols used by the BS 200. Base station controlroutines 224 includes a scheduling module 226, a base station modetransition module 228, an active mode module 230, a transmit standbymode module 232, a receiver control module 234, a transmitter controlmodule 236, and an I/O interface control module 238.

Scheduling module 226, e.g., a scheduler, schedules uplink and downlinksegments to WTs. The scheduling is a function of the mode of operationof the BS 200. In some embodiments, when the BS is in the active mode ofoperation the BS can schedule uplink and downlink traffic channelsegments to WTs, while when the BS is in the transmit standby mode ofoperation, the BS does not schedule any uplink or downlink trafficchannel segments to WTs.

Base station mode transition control module 228 controls the transitionof the BS 200 between the active mode of operation and the transmitstandby mode of operation. The base station mode transition controlmodule 228 uses the data/information 220 in memory 220 including modetransition criteria 270, mode transition schedule information 269,number of active users 253, inactivity time 254, received access signals255, received wake-up signals 256, received handoff signals 257,received state change signals 258, received mode change signals 249and/or the current mode 252 in deciding whether to and at what time totransition between base station operational modes, e.g., active mode totransmit standby mode or transmit standby mode to active mode. As partof the mode transition process, mode transition module 228 activates oneof active mode module 230 and transmit standby module 232, whiledeactivating the other one.

Active mode control module 230 controls BS operations in the active modeof base station operation. Active mode module 230 includes a 1^(st)synchronization signaling module 240, a traffic channel signaling module242, and a 1^(st) paging module 244. First synchronization signalingmodule 240 uses the data/information 220 including active modesynchronization signal info 272 to control the power level and rate ofsynchronization signals, the synchronization signals including beaconsignals and pilot signals. In the active mode of operation, at leastsome of the synchronization signals are controlled to be transmitted atat least one of: (i) a higher power level and (ii) a higher rate, thenwhen the base station is operating in the transmit standby mode ofoperation. In the active mode of operation the base station 200 supportsuplink and downlink traffic channel signaling with the scheduling module226 scheduling uplink and downlink traffic channel segments to activeWTs being serviced by the BS 200, e.g., WTs currently registered withthe BS 200, operating in an active mode of operation, and currentlyhaving a BS assigned WT active user identifier. The uplink and downlinktraffic channel segments are used to convey user data/information. Thetraffic channel signaling module 242 controls operations pertaining tothe encoding, modulation and transmission of downlink traffic channelsignals and controls operations pertaining to decoding, demodulation,and recovery of uplink traffic channel signals. 1^(st) paging module 244controls paging operations in the active mode of base station operation.

Transmit standby mode control module 232 controls BS operations in thetransmit standby mode of base station operation. Transmit standby modemodule 232 includes a 2^(nd) synchronization signaling module 246, and a2nd paging module 244. Second synchronization signaling module 246 usesthe data/information 220 including transmit standby mode synchronizationsignal info 279 to control the power level and rate of synchronizationsignals, the synchronization signals including at least one of beaconsignals and pilot signals. In the transmit standby mode of operation, atleast some of the synchronization signals are controlled to betransmitted at at least one of: (i) a lower power level and (ii) a lowerrate, then when the base station is operating in the active mode ofoperation.

Receiver control module 234 controls operations of receiver 202;transmitter control module controls operations of transmitter 204; I/Ointerface control module controls operations of I/O interface 208. Insome embodiments, modules 234, 236, and/or 238 operate in conjunctionwith either active mode module 230 or transmit standby module 232depending upon the BS's current mode 252 of operation.

Data/information 220 includes WT data information 250 systemdata/information 251, current mode 252, number of active users 253,inactivity time 254, and current transmission power information 259. Atsome times one or more of the following may be included in datainformation 220: received access signal information 255, receivedwake-up signal information 256, received hand-off signal information257, received state change signal information 258, and received modechange signal information 249.

WT data information 250 includes different sets of information atdifferent times depending on the WTs currently being serviced by the BS200. At some times, the BS may not have any users either in sleep oractive state that are currently registered and being serviced. At othertimes, the BS may have one or more users which are being serviced by theBS 200, and WT data/info 250 includes (WT 1 data/information 260, . . ., WT N data/information 261), with each set of data/informationcorresponding to a WT user currently being serviced. WT 1 datainformation 260 includes user data 262, WT identification information264, device/session/resource information 263, and WT user stateinformation 265. User data 262 includes, e.g., voice, video, text, datafile data and information intended for WT 1 and/or intended to be sentto a peer node of WT 1 in a communications session with WT 1. WTidentification information 264 includes identifiers associated with WT1,e.g., a unique device identifier, a base station assigned registereduser identifier, and/or a base station assigned active user identifier.Device/session/resource information 263 includes information identifyingthe type of WT device, e.g., mobile phone, data terminal, model, class,tier, etc., session information including, e.g., routing information,peer node identification information, session time information, etc.,and resource information including, e.g., assigned uplink and/ordownlink traffic channel segments, assigned dedicated control channelsegments, assigned resources for a page directed to WT1, etc. WT userstate information 265 includes information identifying the current stateof operation of WT 1, e.g., sleep state, active-hold ON state, or anactive hold-state.

Current mode 252 includes information identifying the current mode ofoperation of BS 200, active mode or transmit standby mode. Number ofactive users 253 identifies the number of WTs currently registered withBS 200 in an active state of operation. Inactivity time 254 is a timecounter maintained by BS 200 of the amount of time since at least one WTwas active from the perspective of the BS 200. When, the inactivity time254 exceeds a threshold in mode transition criteria 270, the modetransition module 228 transitions the BS from active mode to transmitstandby mode.

Received access signal information 255 represents a detected receivedrequest for access by a WT, e.g., a registration request. In someembodiments, under certain conditions, the received access signal 255may be used by transition module 228 to trigger a transition fromtransmit standby mode to an active mode of operation. For example, the aWT may have entered BS 200's cell and desires to communicate user data,the BS may be in a transmit standby mode, the WT may send an uplinkaccess signal during a contention based access interval, and thisreceived signal may be used a trigger by transition module 228 toactivate transition of the BS 200 into active mode.

Received wake-up signal information 255 represents a detected receivedrequest to transition the base station from transmit standby mode toactive mode. For example, a wireless terminal, by monitoring the powerlevel and/or rate of downlink broadcast synchronization signalsdetermines that the BS 200 is in transmit standby mode, but decides thatit desires to become an active user; therefore, the WT sends a wake-upsignal to the BS. For example, in some embodiments a tone or tones atpredefined times, within the timing/frequency structure, may be reservedto receive the wake-up signal. In some embodiments, the same air linkresources reserved for access signals may also be used for wake-upsignals. In some embodiments, the wake-up signal has a differentcharacteristic than an access signal. In some embodiment, the wake-upsignal is the same as the access signal, with the BS 200 treating thereceived signal differently depending upon its current mode 252.

Received handoff signal 257 includes information associated with ahandoff operation. In some embodiments at some times, the handoff signalmay be communicated via a wireless link with a WT. In some embodimentsat some times, the handoff signal may be communicated via the backhaulnetwork through I/O interface 208, e.g., allowing for more seamlessand/or faster handoff operations. Received handoff signal information257 may be used by BS 200 to update the WT data/information and thenumber of active users 253. For example, if the received handoff signalinformation 257 indicates that the last current active user is beinghanded off to an adjacent base station, the information may be used toupdate number of active users 253 and trigger the start of inactivitytimer 254. As another example, if the received handoff signalinformation 257 indicates that the last currently registered user at BS200, e.g., a user in sleep state, is being handed off to an adjacentbase station, the handoff signal information 257 may be used to triggera transition from active mode to transmit standby mode without waitingfor the inactivity delay timer to reach a transition criteria. As stillanother example, if the received handoff information 257 indicates thatan active WT is to be handed off from an adjacent BS to BS 200, and BS200 is currently in transmit standby mode, the information may be usedto trigger a transition of the base station 200 to active mode, e.g.,such that the BS 200 will be operating in active mode when the WTexecutes the handoff, providing a more seamless handoff operation.

Received mode change signal information 249 includes informationreceived in a commanded mode change message, e.g., from a centralmanagement command node, directing that a base station mode change beexecuted. For example, a central management node may be directing modechanges in accordance with a schedule or in accordance with overallinterference levels, load patterns, priority issues, emergencyconsiderations, etc. As another example, an adjacent base station maysend a commanded mode change message to BS 200.

Received state change signal information 258 includes receivedinformation from a WT indicating a request for a change in state, e.g.,from sleep to active or from active to user. The BS's mode of operationis affected accordingly. For example, if the BS is currently in transmitstandby mode and the BS receives a signal indicating that one of the WTscurrently registered but in sleep state requests to be transitioned toactive state, the transition module 228 may transition the base station200 to active mode. As another example, if the BS is currently in activemode, with only one active WT, and that active WT requests to transitionto sleep state, then the BS sets the number of active users 253 to zeroand starts the inactivity counter, which can result in a transition ofthe base station to transmit standby mode if no other WT becomes activebefore a timeout criteria is reached.

Current transmission power information 259 is information pertaining tothe current transmission of the BS. In accordance with the invention,the BS the average transmission power associated with the transmissionof non-traffic channel signals during the transmit standby mode ofoperation is reduced when compared to the average transmission powerassociated with the transmission of non-traffic channel signals duringthe active mode of operation. For example, by reducing the power levelof each pilot signal during the transmit standby mode of operation,average transmission power is reduced. Alternately, by reducing thenumber of pilot signal tones per OFDM symbol transmission time interval,e.g., from four to one, average transmission power is reduced.Alternately, by skipping OFDM symbol transmission time intervals duringwhich pilot signals are conveyed, average transmission power is reduced.

System data/information 251 includes active mode information 266,transmit standby mode information 267, uplink/downlink timing andfrequency structure information 268, schedule information 269, modetransition criteria information 270, and power information 271.

Active mode information 266 includes synchronization signal information272 including characteristic information associated with thesynchronization signals which are generated and transmitted by the BSwhile in the active mode of operation. Synchronization signalinformation 272 includes beacon signal information 273 and pilot signalinformation 274. Beacon information 273 includes power information 275,e.g., a reference power level associated with the beacon tone or tonesof each beacon signal, and rate information 276, e.g., informationidentifying the transmission rate of the beacon signal, while in theactive mode. Pilot information 274 includes power information 277, e.g.,a reference power level associated with pilot tones, and rateinformation 278, e.g., information which identifies which OFDMtransmission time intervals are used to transmit pilot tones, and howmany pilot tones are communicated simultaneously in each of the OFDMtransmission time intervals in which pilot tones are communicated, whilein active mode.

Transmit standby mode information 267 includes synchronization signalinformation 279 including characteristic information associated with thesynchronization signals which are generated and transmitted by the BSwhile in the transmit standby mode of operation. Synchronization signalinformation 279 includes beacon signal information 280. and pilot signalinformation 281. Beacon information 280 includes power information 282,e.g., a reference power level associated with the beacon tone or tonesof each beacon signal, and rate information 283, e.g., informationidentifying the transmission rate of the beacon signal, while in thetransmit standby mode. Pilot information 281 includes power information284, e.g., a reference power level associated with pilot tones, and rateinformation 285, e.g., information which identifies which OFDMtransmission time intervals are used to transmit pilot tones, and howmany pilot tones are communicated simultaneously in each of the OFDMtransmission time intervals in which pilot tones are communicated, whilein transmit standby mode. In accordance with the present invention, atleast some of the synchronization signals transmitted by the basestation in the transmit standby mode of operation are transmitted atleast one of: (i) a reduced power level and (ii) a reduced rate, withrespect to the active mode of operation. This results in a lowertransmission average power output by the base station while in thetransmit standby mode of operation which results in reduced levels ofinterference from the perspective of adjacent cells which are using thesame frequencies.

Uplink/downlink timing and frequency structure information 268 includes,e.g., uplink carrier frequency, uplink tone block, downlink carrierfrequency, downlink tone block, uplink tone hopping information,downlink tone hopping information, segment definitions in a repetitivetiming and frequency structure, beacon information, pilot information,OFDM symbol transmission timing information, and grouping of OFDMsymbols into, e.g., half-slots, slots, superslots, beaconslots,utraslots, etc. Schedule information 269 includes stored scheduleinformation identifying when to transition the base station betweenactive and transmit standby mode. In various embodiments, scheduleinformation 269 includes data, time, and corresponding mode informationfor a plurality of different times. Schedule information 269 may includepredetermined schedules and/or schedules which can be adjusted. Forexample, BS 200 may be located in a remote low density population regionand schedule information 269 may be based on a train schedules orschedules coordinated to result in the base station being in an activemode coinciding with the expected presence of a train in the basestation's cell. Adjustment information may be communicated to accountfor delays, cancelled trains and/or added unscheduled trains.

Mode transition criteria information 270 includes information such asinactivity time limits utilized by the base station mode transitioncontrol module 228 in determining if and when to perform a mode switch.Power information 271 includes BS power information, e.g., a referenceBS nominal baseline power level, and specific power levels or offsetsfrom the baseline level associated with each of the different types ofsignals to be transmitted by the BS, e.g., beacon, pilot, flashassignment, regular assignment, paging, traffic channel at various datatransmission rates, etc.

FIG. 3 is a drawing of an exemplary wireless terminal (WT) 300implemented in accordance with the present invention and using methodsof the present invention. Exemplary WT 300 may be any of the WTs (112,114,116, 118) of exemplary system 100 of FIG. 1.

Exemplary WT 300 includes a receiver 302, a transmitter 304, a processor306, user I/O devices 308, and a memory 310 coupled together via a bus312 over which the various elements may interchange data andinformation. Receiver 302 is coupled to receive antenna 303 via whichthe WT 300 can receive downlink signals from BSs 200.

When the base station 200 is in the transmit standby mode of operation,the downlink signals include synchronization signals, e.g., beaconsignals and pilot signals at a reduced rate and/or power level. When,the base station 200 is in the active mode of operation the downlinksignals include the synchronization signals, e.g., beacons signals andpilot signals at a higher rate and/or higher power level in comparisonto the transmit standby mode. In the active mode of BS operation, uplinkand downlink traffic channel signaling is supported and the downlinksignals typically also include assignment signals and traffic channelsignals. Receiver 302 includes a decoder 314 which decodes receiveddownlink signals which have been encoded by the base station prior totransmission.

Transmitter 304 is coupled to transmit antenna 305 through which WT 300can transmit uplink signals to BSs 200. In some embodiments, the sameantenna is used for both the receiver and transmitter. Uplink signalscan include access signals, BS wake-up signals, WT state change requestsignals, requests for uplink traffic channel segment resources, handoffsignals, power and timing control signals, and user data signals.Transmitter 304 includes encoder 316 which encodes at least some of theuplink signals prior to transmission.

User I/O devices 308 includes, e.g., switches, microphone, speaker,display, keypad, keyboard, touch-screen, mouse, camera, etc., andprovides an interface for inputting user data/information and outputtingreceived user data/information. User I/O devices 308 also allow theoperator of WT 300 to control at least some operations of the WT, e.g.,initiating a call, initiating a request for a mode change, access storedinformation, powering off, power off, etc.

Memory 310 includes routines 318 and data/information 320. The processor306, e.g., a CPU, executes the routines 318 and uses thedata/information 320 in memory 310 to control the operation of thewireless terminal and implement methods of the present invention.Routines 318 include communications routines 322, which implements thecommunications protocols used by the WT 300, and wireless terminalcontrol routines 324. The WT control routines 324 includes a basestation mode determination module 326, a wake-up signaling module 327,an access signaling module 328, a handoff signaling module 330, a WTstate transitioning module 332, a timing/synchronization module 333, abase station identification module 334, a receiver control module 336, atransmitter control module 338, and a user I/O module 339.

Base station mode determination module 326 uses the data information 320in memory 310 to determine the mode of operation that the BS whichtransmitted the received synchronization signals being evaluated, e.g.,beacon and/or pilot signals, is currently operating in, e.g., transmitstandby mode or active mode. For example, in some embodiments, a reducedrate of pilot tone signaling indicates that the BS is in transmitstandby mode, and detected rate of received pilot tones is used bymodule 326 to determine the mode of the BS. As another example, in someembodiments, a reduced power level of pilot signal indicates that thebase station is in transmit standby mode, and the level of the receivedpilot signals may be compared to the level of the received beaconsignals in performing the determination. In some embodiments, a detectedlevel shift in received pilot tones may be indicative of a base stationmode change. BS mode determination module 326 includes one of more of arelative power level determination module 327 and a rate analysis module329. The BS mode determination module 326 processes receivedsynchronization signals to evaluate at least one of synchronizationsignal power levels and a rate of at least some synchronization signals.Relative power level determination module 327 determines the relativepower level between at least two types of received synchronizationsignals, e.g., pilot tone signals and beacon signals. The rate analysismodule 329 distinguishes between received synchronization signal ratescorresponding to different modes of operation. For example, in someembodiments, the base station uses a different rate of pilot tonesignals for the transmit standby mode and active mode of base stationoperation, and rate analysis module 329 measures the received pilot tonerate and identifies the received pilot tone rate with a mode of basestation operation. In some embodiments, a precise measurement of pilottone rate is not performed, but received signals are processed by rateanalysis module 329 such as to be able to associate a level ofsynchronization signaling with one of the different modes of basestation operation. Relative power level determination module 327 and/orrate analysis module 329 uses as input received synchronization signalinformation 341 and generate as output processed synchronization signalinformation 347.

Base station mode decision module 331 determines the mode of the basestation operation based on the relative power level of at least twodifferent synchronization signals and/or the rate of at least one typeof synchronization signal. For example, processed synchronization signalinformation 347 output from the relative power level determinationmodule 327 and/or the rate analysis module 329 is used by base stationmode decision module 331 in conjunction with BS mode detectioninformation 372 to determine the base station's current mode ofoperation.

In some other embodiments, the base station mode determination module326 determines the mode of operation based on a level of downlinksignaling and/or the omission of one or more of certain types ofsignals. For example, in some such embodiments, the base station modedetermination module 326 determines the mode of base station operationbased on the presence or lack thereof of assignment signalscorresponding to uplink traffic channel segments.

Wake-up signaling module 327 controls the generation and transmission ofwake-up signals to a BS 200, e.g., a BS 200 detected by determinationmodule 326 to be in a transmit standby mode of operation, when WT 300wishes to wake-up the base station, e.g., to register with the basestation, to change to active state from sleep so that the WT may senduplink traffic channel data, etc.

Access signal module 328 controls the generation and transmission ofaccess signals to a BS 200, e.g., during predetermined access intervalsusing predetermined tones in the uplink timing and frequency structure,the access signals not requiring precise timing synchronization andbeing used for initiating a registration request with a base station.Handoff signaling module 330 controls handoff operations pertaining toWT 300 including the control of the generation and transmission ofhandoff request signals to a BS. State transitioning module 332 controlsWT 300 state transition operations and requests for transitions whichare communicated to BS 300, e.g., transitions from WT sleep state to WTactive state, and WT active state to WT sleep state. In someembodiments, the WT active state is further qualified as including anactive-hold and an active on state. Request for state transitions mayinclude state change request signals and requests for air link uplinkresources which may be considered, in some embodiments, as a statechange request. In some embodiments, WT state transitions are tracked bythe BS and used by the BS in determining BS mode transitions.

Timing/synchronization module 333 performs timing synchronization andfrequency synchronization operations, e.g., synchronizing the WTs uplinktransmissions to arrive in synchronization with other WT transmissionsin accordance with an uplink timing and frequency structure beingmaintained by the BS and being referenced with respect to downlinksignaling synchronization signals. In some embodiments, the WT obtains acoarse level of synchronization based on received beacon and/or pilotsignals and communicates BS wake-up signals and/or access signalswithout the need for a high level of timing synchronization.Timing/synchronization module 333 achieves a high level ofsynchronization, e.g., to within a cyclic prefix duration, for regularuplink signaling, including uplink traffic channel signals, communicatedwhile the base station is in an active mode of operation. Base stationidentification module 334 identifies the base station transmitting thesynchronization signals, e.g., beacon signals, and the identificationcan involve determining a network point of attachment associated with abase station, sector, and/or carrier frequency. Receiver control module336 controls receiver 302 operations; transmitter control module 338controls transmitter 304 operations, and user I/O module 339 controlsuser I/O devices 308. Some of the WT control modules may operate inconjunction to perform a specific operation. For example, thetransmitter control module 338 may operate in conjunction with wake-upsignaling module 327 at certain times.

Data/information 320 includes wireless terminal data/information 336,access signal information 338, base station wake-up signal information340, handoff signal information 342, state change signal information344, received synchronization signal information 341, processedsynchronization signal information, and system data/information 350. WTdata/information 336 includes user data 352, device/session/resourceinformation 354, WT identification information 356, WT user stateinformation 358, base station identification information 360, and basestation mode information 362.

User data 352 includes, e.g., data corresponding to voice, video, text,files to be communicated to peers of WT 300 or received from peers of WT300. Device/session/resource information 353 includes identificationinformation of a peer of WT 300 in a communication session with WT 300,routing information, and air link resources information corresponding toWT 300, e.g., information identifying downlink and uplink trafficchannel segments assigned to WT 300, while its presently connected BS isin active mode of operation. WT identification information 356 includesidentifiers associated with and/or assigned to WT 300 including, e.g., abase station assigned registered user identifier, a base stationassigned active user identifier, paging identifier information, and/orgroup identifier information. WT user state information 358 includesinformation identifying whether the WT is a sleep state or an activestate. WT user state information 358, in some embodiments, also includesinformation further identifying whether the WT is in an active-On stateor an active-Hold state. Base station identification information 360includes information identifying the base station being used as the WT'scurrent point of network attachment and/or information identifying a BSthat the WT desires to register with and use as a point of networkattachment. For example, base station ID information 360 may be derivedfrom received beacon signals and/or received pilot signals. Base stationmode information 360 includes information identifying the mode ofoperation for base stations, e.g., for identified base stations. Forexample, at any given time, a base station may be in transmit standbymode of operation, e.g., a sleep mode of operation having reducingoutput signals, lower output power and producing less interference, orthe base station may be in an active mode of operation, e.g.,representing a full-up operational mode and supporting uplink anddownlink traffic channel signaling.

Access signal information 338, including access signal specificationssuch as, e.g., signal characteristics including power level information,modulation signal value information and extension portion information,is used by the access signal module 328 to generate access signals usedfor registering WT 300 with a base station. BS wake-up signalinformation 340, including wake-up signal specifications such as, e.g.,signal characteristics including power level information, modulationsignal value information and extension portion information, is used bythe wake-up module 328 to generate wake-up signals used for waking-up abase station which is in a transmit standby mode of operation. Hand-offsignal information 342, includes information used to generate handoffsignals and information extracted from received hand-off signals. Statechange signal information 344 includes information pertaining to WT 300state changes, e.g., information for state change request messages andinformation indicating that the BS has authorized a WT state change,e.g., allocating the WT an active user identifier.

Received synchronization signal information 341 includes received beaconsignal information 343 and received pilot signal information 345corresponding to received downlink synchronization signals received byreceiver 302. Received synchronization signal information 343 is used aninput to the relative power level determination module 327 and/or therate analysis module 329. Processed synchronization signal information347 includes power level information 349 and rate information 351.Processed synchronization signal information 347 includes informationoutput from the relative power determination module and/or the rateanalysis module 329, which is used as input by the base station modedecision module 331. Power level information 349 includes, e.g., adetermined power level associated with received beacon signal, adetermined power level associated with received pilot tone signals, anda relative power ratio between the two types of received signals. Rateinformation 351 includes, e.g., a determined rate of a received type ofsignals. In some embodiments a determined rate of pilots tone signalsis, e.g., an identified number of pilot tone signals communicatedsimultaneously in one OFDM symbol transmission time interval. Anotherexample of a determined rate of pilot tone signals is, e.g., a ratio ofa first number of OFDM transmission time intervals including pilot tonesignals to a second number of OFDM transmission time intervals duringwhich no pilots tone signals are transmitted.

Received beacon signal information 343 in combination with processedsynchronization signal information 347 includes information pertainingto and/or derived from received beacon signals, e.g., power level of thereceived signal, tones associated with the received beacon, time withina timing structure associated with the received beacon signal, basestation, sector and/or carrier associated with the received beacon.Received pilot signal information 345 in combination with processedsynchronization signal information 347 includes information pertainingto and/or derived form received pilot signals, e.g., power level of thereceived pilots, rate of received pilot signaling including number ofpilots per OFDM symbol transmission time interval and/or fraction ofOFDM symbol transmission time intervals including pilots, relative powerof received pilots with respect to received beacons, and/or base stationidentification information derived from pilots, e.g., a base stationidentifier derived from a pilot slope.

System data/information 350 includes a plurality of sets of base stationinformation (BS 1 information 364, BS N information 366). BS 1information 364 includes active mode information 368, transmit standbymode information 370, base mode detection information 372,uplink/downlink timing and frequency structure information 374, and basestation identification information 376.

Uplink/downlink timing and frequency structure information 374 includes,e.g., uplink carrier frequency, uplink tone block information, uplinktone hopping sequence information, uplink segment information, downlinkcarrier frequency, downlink tone block information, downlink tonehopping sequence information, OFDM symbol transmission time intervalinformation, grouping information of OFDM symbol transmission timeintervals into half-slots, slots, superslots, beaconslots, ultraslots,etc. Active mode information 368 includes information pertaining tosegments, signals, and functions relevant to the active mode, e.g.,traffic channel segments and signals, dedicated control channel segmentsand signals. Transmit standby mode information 370 includes informationpertaining to segments, signals, and functions relevant to the transmitstandby mode, e.g., signals associated with base station wake-upsignaling and wake-up operations. Base station mode detectioninformation 372 includes information used by base station determinationmodule 326 to evaluate received beacons and/or pilots to determine theBS mode of operation. BS mode detection information 372 includes, e.g.,rate information and/or power level information associated with eachmode of BS station operation which may be used to distinguish betweenthe different modes of base station operation. For example, information372 may include the rate of pilot signals in each mode and/or therelative power level of pilot signals with respect to beacon signals ineach mode. Base identification information 376 includes informationwhich allows the BS ID module 334 to determine the BS corresponding toreceived signals, e.g., a set of beacon tones occurring at predefinedfrequencies and/or times within the downlink timing and frequencystructure associated with BS 1 and identifying BS 1 from among aplurality of base stations in the system. Identification may includeidentification of cell, sector and/or carrier frequency used.

FIG. 4 is a drawing 400 of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the active mode. Vertical axis 402represents tone index number (0, 1, 2, . . . 15) in the tone blockutilized for downlink signaling by the base station. Horizontal axis 404represents time, with each unit representing one OFDM symboltransmission time interval. Each small square in the grid represents abasic transmission unit, an OFDM tone-symbol, corresponding to one tonefor the duration of one OFDM symbol transmission time interval. Amodulation symbol may be conveyed corresponding to each OFDM tone-symbolof the grid. Legend 406 indicates that full shading of a grid square, asshown in legend element 408, signifies that a beacon tone signal atpower level P_(B) occupies the tone-symbol. Legend 406 also indicatesthat vertical line shading of a grid square, as shown in legend element410, signifies that a pilot tone signal at power level P_(P) occupiesthe tone-symbol.

FIG. 5 is a drawing 500 of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the transmit standby mode, for an exemplaryembodiment. The base station may be the same base station correspondingto the description of FIG. 4, but now operating in the transmit standbymode rather than the active mode. Vertical axis 502 represents toneindex number (0, 1, 2, . . . , 15) in the tone block utilized fordownlink signaling by the base station. Horizontal axis 504 representstime, with each unit representing one OFDM symbol transmission timeinterval. Each small square in the grid represents a basic transmissionunit, an OFDM tone-symbol, corresponding to one tone for the duration ofone OFDM symbol transmission time interval. A modulation symbol may beconveyed corresponding to each OFDM tone-symbol of the grid. Legend 506indicates that full shading of a grid square, as shown in legend element508, signifies that a beacon tone signal at power level P_(B) occupiesthe tone-symbol. Legend 506 also indicates that horizontal line shadingof a grid square, as shown in legend element 510, signifies that a pilottone signal at power level P_(PR) occupies the tone-symbol, whereP_(PR)<P_(P). In this exemplary embodiment, by reducing the power levelof each pilot signal communicated the overall average transmission powerof the base station is reduced in the transmit standby mode of operationwith respect to the active mode of operation.

FIG. 6 is a drawing 600 of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the transmit standby mode, for anotherexemplary embodiment. The base station may be the same base stationcorresponding to the description of FIG. 4, but now operating in thetransmit standby mode rather than the active mode. Vertical axis 602represents tone index number (0, 1, 2, . . . , 15) in the tone blockutilized for downlink signaling by the base station. Horizontal axis 604represents time, with each unit representing one OFDM symboltransmission time interval. Each small square in the grid represents abasic transmission unit, an OFDM tone-symbol, corresponding to one tonefor the duration of one OFDM symbol transmission time interval. Amodulation symbol may be conveyed corresponding to each OFDM tone-symbolof the grid. Legend 606 indicates that full shading of a grid square, asshown in legend element 608, signifies that a beacon tone signal atpower level P_(B) occupies the tone-symbol. Legend 606 also indicatesthat vertical line shading of a grid square, as shown in legend element610, signifies that a pilot tone signal at power level P_(P). In FIG. 4,28 successive OFDM symbol transmission time intervals are shown. In FIG.4, three of the OFDM symbol transmission time intervals include onebeacon tone signal and no pilot signals, while the other 25 OFDM symboltransmission time intervals each include 4 pilot tone signals. Incomparison in FIG. 6, the three beacon signal OFDM symbol transmissiontime intervals remain unchanged; however, the pilot signaling has beenreduced. In FIG. 6, seven OFDM symbol transmission time intervalsinclude 4 pilot signals each, while the other 18 OFDM symboltransmission time intervals include zero pilot signals. In thisexemplary embodiment, by reducing the rate of pilot signaling, theoverall average transmission power of the base station is reduced in thetransmit standby mode of operation with respect to the active mode ofoperation.

FIG. 7 is a drawing 700 of an exemplary time frequency grid representingdownlink air link resources available to a base station, implemented inaccordance with the present invention, and indications of timingsynchronization signals transmitted by the base station using thoseresources while operating in the transmit standby mode, for stillanother exemplary embodiment. The base station may be the same basestation corresponding to the description of FIG. 4, but now operating inthe transmit standby mode rather than the active mode. Vertical axis 702represents tone index number (0, 1, 2, . . . , 15) in the tone blockutilized for downlink signaling by the base station. Horizontal axis 704represents time, with each unit representing one OFDM symboltransmission time interval. Each small square in the grid represents abasic transmission unit, an OFDM tone-symbol, corresponding to one tonefor the duration of one OFDM symbol transmission time interval. Amodulation symbol may be conveyed corresponding to each OFDM tone-symbolof the grid. Legend 706 indicates that full shading of a grid square, asshown in legend element 708, signifies that a beacon tone signal atpower level P_(B) occupies the tone-symbol. Legend 706 also indicatesthat vertical line shading of a grid square, as shown in legend element710, signifies that a pilot tone signal at power level P_(P). In FIG. 4,28 successive OFDM symbol transmission time intervals are shown. In FIG.4, three of the OFDM symbol transmission time intervals include onebeacon tone signal and no pilot signals, while the other 25 OFDM symboltransmission time intervals each include 4 pilot tone signals. Incomparison in FIG. 7, the three beacon signal OFDM symbol transmissiontime intervals remain unchanged, however, the pilot signaling has beenreduced. In FIG. 7, 25 OFDM symbol transmission time intervals includeonly one pilot tone signal each. In this exemplary embodiment, byreducing the rate of pilot signaling, the overall average transmissionpower of the base station is reduced in the transmit standby mode ofoperation with respect to the active mode of operation.

FIG. 15 is a drawing 1500 of an exemplary time frequency gridrepresenting downlink air link resources available to a base station,implemented in accordance with the present invention, and indications oftiming synchronization signals transmitted by the base station usingthose resources while operating in the transmit standby mode, for stillanother exemplary embodiment. The base station may be the same basestation corresponding to the description of FIG. 4, but now operating inthe transmit standby mode rather than the active mode. Vertical axis1502 represents tone index number (0, 1, 2, . . . , 15) in the toneblock utilized for downlink signaling by the base station. Horizontalaxis 1504 represents time, with each unit representing one OFDM symboltransmission time interval. Each small square in the grid represents abasic transmission unit, an OFDM tone-symbol, corresponding to one tonefor the duration of one OFDM symbol transmission time interval. Amodulation symbol may be conveyed corresponding to each OFDM tone-symbolof the grid. Legend 1506 indicates that full shading of a grid square,as shown in legend element 1508, signifies that a beacon tone signal atpower level P_(B) occupies the tone-symbol. In FIG. 4, 28 successiveOFDM symbol transmission time intervals are shown. In FIG. 4, three ofthe OFDM symbol transmission time intervals include one beacon tonesignal and no pilot signals, while the other 25 OFDM symbol transmissiontime intervals each include 4 pilot tone signals. In comparison in FIG.15, the three beacon signal OFDM symbol transmission time intervalsremain unchanged, however, the pilot signaling has been eliminated. Inthis exemplary embodiment, by reducing the rate of pilot signaling tozero, the overall average transmission power of the base station isreduced in the transmit standby mode of operation with respect to theactive mode of operation.

FIG. 4-7 and 15 have been provided to explain the concepts ofsynchronization signaling power and/or rate reduction in accordance withthe present invention. The characteristics of the air link resources,types of synchronization signaling, amounts of power reduction, and/oramounts of rate reduction may vary depending upon the type of system,and specifications of the system.

In one exemplary OFDM wireless communications system for a base stationoperating in the active mode, e.g., an OFDM symbol transmission timeinterval is approximately 100 micro-sec, a downlink tone block comprises113 contiguous tones, a beacon signal occupies one tone for twosuccessive OFDM symbol transmission time intervals, beacon signals occuronce during a beacon slot of 912 OFDM symbol transmission time intervalsand 4 pilot tone signals may be communicated during each of 896 OFDMsymbol transmission time intervals during a beacon slot, and the pilotsignals account for approximately 18% of the base station transmissionpower. In some such exemplary systems, a base station operating in atransmit standby has a reduced level of pilot signaling, e.g., one pilottone signal for every eight OFDM symbol transmission time intervalswhere, in the active mode, there were previously pilot tone symbolstransmitted. This exemplary transmit standby mode of base stationoperation corresponds to one pilot tone signal for each of 112 OFDMsymbol transmission time intervals in a beacon slot. In some suchexemplary embodiments, beacon signaling is unaltered between the twomodes of base station operation. Although the beacon signal is typicallytransmitted at a much higher power level than a pilot signal, it iscommunicated much less frequency and the energy is concentrated on oneor a few tones, thus limiting the interference damage. However, pilotsare communicated much more frequently and consume a significant portionof the base station transmit power while in the active mode; therefore,reducing or limiting pilot signaling in the transmit standby mode canachieve more beneficial interference reductions. In addition, in somesuch embodiments, the base station does not transmit downlink trafficsignals while operating in the transmit standby mode of operation,thereby additionally decreasing base station transmit power andinterference levels.

In another type of wireless communication system, e.g., a CDMA system,spreading codes synchronization signals may be used, and the power leveland/or number of spreading code synchronization signals are reduced whenoperating in the transmit standby mode of operation as compared to theactive mode of operation.

FIG. 8 is a drawing 800 illustrating an exemplary base station, BS K804, with cellular coverage area, cell K 802. Cell K 802 includes twoexemplary wireless terminals (WT A 806, WT B 807) coupled to BS K 804via wireless links (808, 809), respectively. BS K 804 may be inaccordance with exemplary BS 200 of FIG. 2, while WT A and WT B may bein accordance with exemplary WT 300 of FIG. 3. BS K 804 is currently inan active mode of base station operation; WT A 806 is in an active-Onstate of WT operation; WT B 807 is in an active-Hold state of WToperation.

FIG. 9 is a drawing 900 illustrating an exemplary base station, BS L904, with cellular coverage area, cell L 902. Cell L 902 includesexemplary two wireless terminals (WT C 906, WT D 908). BS L 904 may bein accordance with exemplary BS 200 of FIG. 2, while WT C 906 and WT D908 may be in accordance with exemplary WT 300 of FIG. 3. WT C 906 andWT D 908 are currently in an off state. There are no WTs in cell Lcurrently being serviced by BS L 904, and the base station L 904 iscurrently operating in the transmit standby mode of operation.

FIG. 10 is a drawing 1000 illustrating an exemplary base station, BS P1004, with cellular coverage area, cell P 1002. Cell P 1002 includesexemplary two wireless terminals (WT E 1006, WT F 1008). BS P 1004 maybe in accordance with exemplary BS 200 of FIG. 2, while WT E 1006 and WTF 1008 may be in accordance with exemplary WT 300 of FIG. 3. BS P 1004is currently operating in a transmit standby mode of operation. WT E1006 is currently off and is not being serviced by BS P 1004. WT F 1008is currently in a sleep state of operation and is coupled to BS P 1004via wireless link 1010. There are currently no WTs in cell P 1002 beingserviced by BS P 1004 that are in an active state of operation.

FIG. 11 is a drawing of a table 1100 illustrating characteristics ofbase station active mode of operation and the base station transmitstandby mode of operation for an exemplary embodiment, in accordancewith the present invention. First information column 1102 listsinformation pertaining to the base station active mode of operation.Second information column 1104 lists information pertaining to the basestation transmit standby mode of operation. First row 1106 identifiesthat in the base station active mode the BS can service WTs in theactive mode and WTs in the sleep mode, while in the BS transmit standbymode of operation the BS can service WTs in the sleep mode of operation.

Second row 1108 identifies that beacon signals are communicated in boththe active mode of operation and the transmit standby mode of operationin this exemplary embodiment. In this embodiment, the beacon signalingis the same regardless of the base station mode of operation. In someembodiments, the beacon signal is a relatively high power signaloccupying one or a few, e.g., two or three or four, tones for a few,e.g., one or two or successive OFDM symbol transmission time intervals.In some such embodiments, the other tones of the downlink tone block areleft unused during the beacon signal transmission. In some embodiments,the beacon signaling may be different in the two modes such that thepower and/or rate is reduced in the transmit standby mode as compared tothe active mode. In some embodiments, a beacon signal may include one ora few high power tones and a larger number of low power tones, e.g., 25to 75 tones out of a tone block of 113 tones, being communicated duringthe same OFDM symbol transmission time interval or intervals. In somesuch embodiments, in the transmit standby mode of operation the highpower tone may unaffected, but the rate and/or power level of the lowerpower tones may be reduced with respect to active mode.

Third row 1110 identifies that pilot signals are communicated in boththe active mode and the transmit standby mode of operation; however, thetransmission rate of the pilot signals and power level of the pilotsignals is reduced in the transmit standby mode with respect to theactive mode, in this exemplary embodiment. In some embodiments, one of:(i) pilot signal power level and (ii) rate of pilot signaling is reducedin the transmit standby mode of operation with respect to the activemode of operation.

Fourth row 1112 indicates that uplink and downlink traffic channel datais communicated in the base station active mode, but not in the basestation transmit standby mode of operation, in this exemplaryembodiment.

Fifth row 1114 indicates that paging signals are communicated in boththe active mode and transmit standby mode of operation. In someembodiments, the paging signaling may be communicated at different ratesand/or have different characteristic depending upon the mode of basestation operation. For example, in active mode, paging opportunities mayoccur more frequently than in the transmit standby mode. In addition, insome embodiments paging signals in the active mode may convey moreinformation and/or be structured to allow for a more rapid response bythe WT to which the page is directed.

FIG. 12 is a drawing 1200 illustrating an exemplary communicationssystem, implemented in accordance with the present invention and usingmethods of the present invention. FIG. 12 includes a plurality of basestations (BS 1 1210, BS 2 1212, BS 3 1214), each with a correspondingcellular coverage area (cell 1 1216, cell 2 1218, cell 3 1220),respectively. Train track 1202 is shown with exemplary train 1204situated on the track 1202. In general, more than one train may beoperating in the area covered by the communications system at the sametime. Exemplary train 1204 includes a plurality of mobile nodes (MN 11206, MN N 1208).

The exemplary communications system also includes a network node 1222coupled to (BS 1 1210, BS 2 1212, BS 3 1214) via wireless links (1226,1228, 1230), respectively. Network node 1222 is coupled to other networknodes and/or the Internet via network link 1232. Network links (1226,1228, 1230, 1232) may be, e.g., fiber optic links, cable link, and/orhigh capacity wireless links such as directed microwave links. Networknode 1222 includes schedule information 1224.

The schedule information 1224 includes train schedule information, e.g.,identifying when a train or trains will be within each BS's cellularcoverage area. The network node 1222 by communicating scheduleinformation and/or information derived from the schedule information tothe BSs, can affect the switching of the base stations from transmitstandby to active mode and from active mode to transmit standby mode.For example, the network node 1222 can send schedule information to eachBS and the BS can switch accordingly. Alternatively, the network nodecan use to the schedule information to determine when to issue modeswitch command signals to each base station to command base station modeswitching operations.

In some embodiments, information derived from train tracking and/ortrain position detection mechanisms such as track sensors, e.g., alreadyin place and used to prevent collisions, is used in controlling thetransitioning of base stations from active to transmit standby mode andfrom transmit standby mode to active mode. In some embodiments, there isa controlled base station mode transitioning of base stations along thetrack 1202, e.g., directed by network node 1222 taking into account thecurrent position of train 1204, the direction of train 1204, and thespeed of train 1204.

Consider, as an example, that the area of track 1202 which runs throughcells 1216, 1218, and 1220 is a rather remote rural area, with a verylow population density. In such an embodiment, when train 1204 is not ina cell (1216, 1218, 1220), it may be advantageous to put the basestation (1210, 1212, 1214) in a transmit standby mode of operation, thusreducing transmit power and reducing interference; however when thetrain is about to enter or is in the cell (1216, 1218, 1220) it may beadvantageous to have the base station operating in active mode. In someembodiments, there can be a linkage along the track with adjacent basestations transitioning between modes as the trains MNs (1206, 1208) arehanded off from one base station to the next. The reduced interferencemay be particularly beneficial in cell boundary areas, e.g., in a cellboundary area bordering on a higher population region where anotheradjacent base station may be typically operated continuously in theactive mode of operation.

In some embodiments, under some conditions base stations are commandedinto transmit standby mode when a train is at or near a specificlocation, e.g., a bridge or tunnel, e.g., for security purposes.

The methods described with respect to the train embodiment of FIG. 12are also applicable to other transportation networks. For example basestations may be situated along flight paths and base station modeoperation transitioning may be coordinated with flight scheduleinformation.

FIG. 13 comprising the combination of FIG. 13A, FIG. 13B, and FIG. 13Cis a flowchart 1300 of an exemplary method of operating a base stationin accordance with the present invention. The exemplary base station maybe base station 200 of FIG. 2. The exemplary method starts in step 1302,where the base station is powered on and initialized. Operation proceedsfrom step 1302 to step 1306, step 1308, and via connecting node A 1303to step 1304.

In step 1306, the base station is set to active mode, and then in step1310, the base station is operated in the active mode of operation. Theoperations of step 1310 include during a first period of timetransmitting synchronization signals at a first rate. For example, thesynchronization signals may include a combination of beacon signals andpilot signals. In some embodiments, the active mode of operation may beconsidered a base station full-up operational state of operation capableof supporting one or more active users and supporting uplink anddownlink traffic channel signaling. The first rate of synchronizationsignaling may be such to support relatively fast synchronization andchannel estimation for WTs being serviced by the. base station.Operation proceeds from step 1310 to step 1312.

In step 1312, the base station is operated to check as to whether thereare any WTs being serviced in an active state. For example, WTs mayregister with a base station that it wishes to use as its point ofnetwork attachment. An exemplary registered wireless terminal may be indifferent states at different times, e.g., a sleep state or an activestate; the active state may be further qualified to include anactive-Hold state and an active-On state. The BS may control the WTstransitioning into the active state, and the control operations mayinclude assigning WTs active user identifiers. The BS may track thenumber of users currently in active state. If in step 1312, it isdetermined that there are no WTs being serviced in an WT active state,e.g., no WTs currently registered with the BS being serviced arecurrently in the active state, then operation proceeds to step 1314;otherwise, operation proceeds to step 1316. In step 1316, the basestation having determined that there is at least one registered WT inthe active state, resets the inactivity timer. Operation proceeds fromstep 1316 back to step 1312, where the base station again checks to seeif there are any WTs being serviced in the active state.

In step 1314, an inactivity timer is incremented. Operation proceedsfrom step 1314 to step 1318. In step 1318, the base station checks as towhether the inactivity timer has exceeded a predetermined limit. If thetimer has exceeded the predetermined limit, operation proceeds to step1320; otherwise, operation returns to step 1312, where the base stationagain checks as to whether or not there are any WTs being serviced in anactive state.

In step 1320, the base station is operated to transition the basestation to a transmit standby mode of operation. The transmit standbymode of operation is a state of base station operation in which the basestation is not servicing active users, but may be servicing users in asleep state, and in which the base station is operated to have a loweraverage output power than in the active mode, thus creating lessinterference in the system. Operation proceeds from step 1320 to step1322. In step 1322, the base station is operated in a transmit standbymode of operation which includes during a second period of time duringwhich synchronization signals are transmitted, the synchronizationsignals are transmitted at least one of: (i) a lower rate than in theactive mode of operation, and (ii) a lower power level, than thesynchronization signals transmitted in the active mode. In someembodiments, some of the synchronization signals, e.g., beacon signals,may be the same in both modes of base station operation, while othersynchronization signals, e.g., pilot signals, may be reduced in powerlevel and/or rate while in the transmit standby mode of operation.

Returning to step 1304, in step 1304, the base station is operated totrack current time. Operation proceeds from step 1304 to step 1324. Instep 1324, the base station checks as to whether the current timeindicates that the base station should be mode transitioned according toschedule information. For example, the BS may be located in a remoterural area and may be transitioned between modes depended upon whetheror not a train including mobile wireless terminals is currently withinthe vicinity of its cellular coverage area based upon train scheduleinformation either stored and/or communicated to the base station. Ifthe current time does not indicate that the base station should be modetransitioned, operation proceeds from step 1324, back to step 1304.However, if the current time indicates that a mode transition should beperformed based upon schedule information, then operation proceeds fromstep 1324 to step 1326.

In step 1326, the base station is operated to determine whether thetransition should be to an active mode in which case operation proceedsto step 1328 or to a transmit standby mode in which case operationproceeds to step 1330. In step 1328, the base station checks as towhether the BS is already in an active state in which case no furtheraction is needed with regard to this transition. However, if in step1328, it is determined that the BS is not in an active mode, thenoperation proceeds from step 1328 to step 1332, where the base stationis operated to transition to an active mode. Operation proceeds fromstep 1332 via connecting node F 1334 to step 1310, where the basestation is operated in active mode.

Returning to step 1330, in step 1330, the base station checks as towhether the BS is already in a transmit standby mode in which case nofurther action is needed with regard to this transition. However, if instep 1330, it is determined that the BS is not in an transmit standbymode, then operation proceeds from step 1330 via connecting node G 1336to step 1320, where the base station is operated to transition to thetransmit standby mode.

Returning to step 1308, in step 1308 the base station is operated toreceive signals over wireless links and the backhaul network interfaceon an ongoing basis. Operation proceeds from step 1308 via connectingnodes (B 1338, C 1346, D 1352, E 1364, J 1365) to steps (1340, 1348,1354, 1366, 1367), respectively.

In step 1340, the base station monitors for access signals from WTsseeking to register with the BS to use the base station as its point ofnetwork attachment. Operation proceeds from step 1340 to step 1342,where the base station checks as to whether or not an access signal hasbeen received. If an access signal has not been received operationreturns to step 1340; otherwise operation proceeds via connecting node H1344 to step 1328, where the BS checks as to whether of not the BS iscurrently in active mode.

Returning to step 1348, in step 1348, the base station monitors forwake-up signals, e.g., via wireless links from WTs and/or via thebackhaul network. A wake-up signal via the backhaul network mayoriginate from a WT, from a centralized command node or from anothernetwork node such as an adjacent base station. For example, a wirelessterminal currently connected to another adjacent BS, expecting toshortly implement hand-off operations resulting in a hand-off to thebase station that it is seeking to wake-up, may initiate the wake-upsignal and communicate the signal via its current point of networkattachment. The WT may initiate this wake-up signal so as to obtainuninterrupted user data communications, and the wake-up signalinformation is ultimately communicated to the BS in transmit standbymode via the backhaul network. As another example, a centralized networkcontrol node may send the BS a wake-up signal via the backhaul, e.g.,the centralized control node implementing control in accordance withtrain schedule information. As another example, another base station,e.g., an adjacent base station, being aware of active mobile usersapproaching the BS's outer cell perimeter may send the BS a wake-upsignal via the backhaul, so that the BS can be transitioned into theactive mode and ready for the active mobile users when they arrive inits cell. As still another example, a WT in the base stations cellularcoverage area either recently powered on or in the sleep state may havedetected that the BS is in a transmit standby mode, and the WT generatesand sends a wake-up signal to the BS via a wireless channel. Operationproceeds from step 1348 to step 1350, where the base station checks asto whether or not a wake-up signal has been received. If a wake-upsignal has not been received operation returns to step 1348; otherwiseoperation proceeds via connecting node H 1344 to step 1328, where the BSchecks as to whether of not the BS is currently in active mode.

Returning to step 1354, in step 1354, the base station monitors forhand-off signals, e.g., via wireless links from WTs and/or via thebackhaul network. Operation proceeds from step 1354 to step 1356, wherethe base station checks as to whether or not a hand-off signal has beenreceived. If a handoff signal has not been received operation returns tostep 1354; otherwise operation proceeds to step 1358. In step 1358 thebase station determines whether or not an operational mode change shouldbe implemented as a result of the received handoff signal. For example,consider that the received handoff signal is via a wireless link fromthe last currently registered wireless terminal being serviced by thebase station, then after completing the handoff the base station can betransitioned into the transmit standby mode of operation. However, ifsuch a received handoff signal was received while other registered WTswere still in an active state within the cell, a base station modechange would not be appropriate. As another example, consider that thehandoff signal is via the backhaul network, indicating that an activewireless terminal is seeking to be handed off to the base station andthat the base station is currently in a transmit standby mode ofoperation. Under such conditions it would be appropriate to transitionthe base station into active mode. However, if the base station wasalready in an active mode when such a handoff signal was received viathe backhaul network no base station mode transition would be needed. Ifin step 1358 the base station determines that a mode change shouldresult, operation proceeds to step 1360; otherwise, no furtheroperations are performed to initiate a mode change in response to thisreceived handoff signal.

In step 1360, the base station proceeds depending upon which modetransition direction. If the mode transition is to the active mode,operation proceeds from step 1360 via connecting node 1 1362 to step1332. If the mode transition is to the transmit standby mode, operationproceeds from step 1360 via connecting node G 1336 to step 1320.

Returning to step 1366, in step 1366, the base station monitors forstate change signals, e.g., via wireless links from currently registeredWTs. For example a registered WT may request to be transitioned fromsleep state to active state so that it may transmit and receive userdata. Operation proceeds from step 1366 to step 1368, where the basestation checks as to whether or not a state change request signal hasbeen received. In some embodiments, a request for additional air linkresources, e.g., a request for a traffic channel segment may be viewedas a state change request signal. If a state change signal has not beenreceived operation returns to step 1366; otherwise operation proceeds tostep 1370. In step 1370 the base station determines whether or not anoperational mode change should be implemented as a result of thereceived WT state change signal. For example, consider that the statechange signal is from a currently registered wireless terminal beingserviced by the base station in sleep state requesting a change toactive state, and the base station is currently in transmit standbymode, then the BS should implement a mode change to active. However, ifsuch a received WT state change signal was received while the basestation was already in the active mode, a base station mode change wouldnot be necessary. If in step 1370 the base station determines that amode change should result, operation proceeds to step 1360; otherwise,no further operations are performed to initiate a base station modechange in response to this received WT state change request signal.

Returning to step 1367, in step 1367, the base station monitors for modechange signals, e.g., a command via the backhaul network indicating thatthe BS should change its operational mode. For example a network controlmode or adjacent base station node may have decided to temporarilycommand the BS out of active mode and into transmit standby mode due toany of a number of conditions such as interference testing, loadconditions, schedule, security considerations, etc. Operation proceedsfrom step 1367 to step 1369, where the base station checks as to whetheror not a mode change request signal has been received. If a mode changesignal has not been received operation returns to step 1367; otherwiseoperation proceeds to step 1371. In step 1371 the base stationdetermines whether or not an operational mode change should beimplemented as a result of the received base station state changesignal. For example, different criteria for a mode change may applydepending upon the source of the mode change signal and or the currentconditions of the base stations. Some received mode change signals areconsidered commands which the base station implements without furtherconsideration, while other received mode change signals are consideredrequests, in which the base station has discretion regarding the modechange. For example, if the mode change command was by a centralizedcontrol node and issued for security reasons, the mode change may beimplemented without further consideration. Alternatively, if the modechange signal was a suggestion to transition to transmit standby mode,based upon a schedule, e.g., a train schedule, and there happens to beadditional registered active users outside the train, the command may beignored by the base station. If in step 1371 the base station determinesthat a mode change should result, operation proceeds to step 1360;otherwise, no further operations are performed to initiate a mode changein response to this received BS mode change signal.

FIG. 14 is a drawing 1400 of a state diagram for an exemplary basestation implemented in accordance with the present invention. Theexemplary base station may be base station 200 of FIG. 2. The exemplarybase station includes an exemplary state 1 1402, otherwise referred toas the base station active mode of operation, and an exemplary state 21404, otherwise referred to as a base station transmit standby mode ofoperation. The arrows indicate conditions for causing a transition ofstate. A state transition from the base station active mode of operation1402 to the base station transmit standby mode of operation 1404 can bea response to: a detected period of inactivity 1406, schedulinginformation 1408, a received base station mode change signal 1409, adetected transition of at least one wireless terminal from an active toa sleep state 1410, e.g., the transition resulting in all wirelessterminal currently registered with the base station being in a sleepstate. A state transition from the base station transmit standby mode ofoperation 1404 to the base station active mode of operation 1402 can bea response to: scheduling information 1412, a received access signal1414, a received wake-up signal 1416, a received hand-off signal 1418, areceived WT state change signal 1420, e.g., state change request signal,or a received base station mode change signal 1422.

FIG. 16 is a drawing 1600 illustrating a series of time sequentialoperations in an exemplary embodiment of the present invention. Diagrams(1601, 1603, 1605, 1607, 1609, and 1611) each represent successive timesequential operations for exemplary cell A 1602. Diagram 1601illustrates that cell A 1602 includes exemplary base station A 1604,operating in a transmit standby mode of operation, sometimes referred toa sleep mode of base station operation. For this exemplary BS 1604,while operating in the transmit standby mode of operation, the BS 1604transmits beacon signals 1606, but does not transmit pilot signals.

Diagram 1603 illustrates that WT A 1608 has entered the cell or poweredon in the cell and has received the beacon signal 1606. The WT 1608identifies BS A 1604 from recovered beacon signal information andrecognizes that the BS 1604 is in transmit standby mode, e.g., from alack of pilot signals.

Diagram 1605 illustrates that the WT 1608 sends a wake-up signal 1610 toBS A 1604. Wake-up signal 1610 is implemented for easy detection withoutthe need for precise timing synchronization, e.g., a relatively highpower signal at a known location in the uplink timing and frequencystructure with a duration of two OFDM symbol transmission timeintervals. In some embodiments, wake-up signal 1610 is implemented foreasy detection without the need for any timing synchronization betweenthe WT 1608 and the BS 1604, e.g., with the BS in transmit standby modecontinuously monitoring certain predetermined tones for a wake-upsignal. In some embodiments, the wake-up signal 1610 has the samecharacteristics as an access signal typically used for registration withan active base station.

Diagram 1607 indicates that the base station 1604 has recognized thewake-up signal 1610 and transitioned into the active mode of operation,e.g., reactivating the normal channels used for control and user datasignaling including pilot signals 1612. Diagram 1609 indicates that theWT 1608 has recognized that the BS 1604 is in the active mode ofoperation, and the WT 1608 has transmitted an access request signal1614, e.g., during one of the access intervals in the uplink timing andfrequency structure using a contention based access segment. Diagram1611 indicates that conventional registration of WT A 1608 has completedand the WTA 1608 has been accepted as an active user by BS A 1604. BS A1604 is assigning WT A uplink and downlink traffic channel segments viawhich user data signals 1616 are being communicated.

FIG. 17 is a drawing 1700 illustrating a portion of an exemplary OFDMuplink timing and frequency structure. At the base station, the uplinktiming can be referenced with respect to the downlink timing, e.g., withrespect to a downlink beacon signal. Vertical axis 1702 indicates uplinktones and includes an uplink tone block 1701, e.g., of 113 contiguoustones. Horizontal axis 1704 represents time. The uplink timing structureincludes access intervals 1706, 1706′ and regular uplink signalingintervals 1708. The access intervals, e.g., access interval 1706, can beused for access signals, e.g., registration request signals, andbase-station wake-up request signals. In some embodiments, dependingupon the base station mode of operation, at least some of thetone-symbols of the access interval are used for different purposes. Atleast some of the signals transmitted by a WT during the access intervalneed not be precisely timing synchronized with respect to the basestation, while signals transmitted by a WT during the regular uplinksignaling interval 1708 typically have precise timing synchronization,e.g., to within a cyclic prefix duration. In some embodiments, signalingduring the access interval uses contention based segments, whilesignaling during the regular uplink signaling interval uses allocated orassigned segments. The regular uplink signaling intervals can be usedfor various signaling including assigned uplink traffic channel segmentsignaling and uplink dedicated control channel signaling.

FIG. 18 is a drawing 1800 illustrating exemplary access interval uplinkair link resources, exemplary segments and exemplary signalingcorresponding to a base station active mode of operation and a basestation transmit standby mode of operation, in accordance with someembodiments of the present invention. Time frequency grid 1802 includes48 tone-symbols, each tone-symbol represented by a small square blockand each tone-symbol representing the uplink air link resources of onetone for one OFDM symbol transmission time interval. Time frequency grid1802 includes a uplink tone block 1804 of 16 contiguous tones (tone 0,tone 1, . . . , tone 15), and has a time duration of an access interval1806, where the access interval includes three consecutive OFDM symboltransmission time intervals (1808, 1810, 1812). In some embodiments, theaccess interval has a different duration, e.g., 8 consecutive OFDMsymbol transmission time intervals.

Time frequency grid 1814 represents time frequency grid 1802partitioned, during the base station active mode of operation, toinclude two access segments. In some embodiments a portion of the uplinkair link resources during the access interval is reserved for accesssegments. Legend 1816 indicates that tone-symbols which are a member ofthe 1^(st) access segment are indicated by cross-hatched shading 1820,while tone-symbols which are a member of the 2^(nd) access segment areindicated by vertical and horizontal line shading 1822. During the basestation active mode of operation, a wireless terminal seeking toregister with the base station and use the base station as its point ofnetwork attachment uses one of the access segments to transmit an accessrequest signal. In some embodiments, the WT randomly selects one of theaccess segments to use to communicate its uplink access registrationrequest signal. Time frequency grid 1814′ represents time frequency grid1814, but also includes an additional access request signal representedwith diagonal line shading 1824. The access request signaling istransmitted at per tone power level P_(AC), and the WT need not beprecisely timing synchronized with respect to the base station, e.g.,timing synchronization error may be greater than an OFDM symbol cyclicprefix duration, but is sufficiently small such that the access requestsignal can be recognized by the base station and should be received atthe base station within the time constraints of the access segment.

Time frequency grid 1826 represents time frequency grid 1802, during thebase station transmit standby mode of operation; grid 1826 includes atleast one wake-up segment. Legend 1828 indicates that tone-symbols whichare a member of the wake-up segment are represented by dotted shading1830. During, the base station transmit standby mode of operation, awireless terminal seeking to wake-up the base station, resulting in thebase station transitioning from transmit standby mode to active mode,uses the wake-up segment to transmit a wake-up signal. Time frequencygrid 1826′ represents time frequency grid 1826, but also includes anadditional wake-up signal represented with vertical line shading 1832.The wake-up signaling is transmitted at per tone power level P_(WU),where P_(WU)>P_(AC) for the same WT, at the same location with the samedetected beacon signal, and having the same amount of remaining batterypower. The WT need not be precisely timing synchronized with respect tothe base station, e.g., timing synchronization error may be greater thanan OFDM symbol cyclic prefix duration, but sufficiently small such thatthe wake-up signal can be recognized by the base station and should bereceived at the base station within the time constraints of the wake-upsegment. In accordance with some embodiments of the present invention,the number of tones used concurrently for the wake-up signal is reduced,e.g., to one, from the number of tones used concurrently for an accessrequest signal, allowing the WT to significantly increase the per tonetransmission power of a wake-up signal increasing the likelihood that abase station will successfully detect a wake-up signal.

In some embodiments in the transmit standby mode of operation, the basestation turns off all transmission signaling except a minimum set ofsignaling that the wireless terminals may use to detect the presence ofthe base station and/or determine a coarse level of synchronization. Insome such OFDM embodiments this minimum set of signaling is the beaconsignaling, and the beacon signals may be communicated at the same orreduced power levels with respect to the active mode of operation. Insome OFDM embodiments, this reduced set of signals can be beacons andpilots with the pilots being transmitted at reduced power and/or ratewith respect to signaling in the active mode. In some embodiments, awireless terminal after detecting the base station, e.g., via a receivedbeacon, and desiring to wake-up the base station sends a wake-up signalto the base station; the base station upon detecting the wake-up signalreactivates the normal channels transitioning the base station into anactive mode of operation. In various embodiments, the wake-up signal isdesigned for easy detection without the need for timing synchronizationor precise timing synchronization. For example, in an exemplary OFDMembodiment, the wake up signal can be a double symbol tone at a knownlocation in the uplink timing and frequency structure. In someembodiments, the wake-up signal can be a signal communicated at arelatively high uplink transmission power level, the signal being longerin duration than the normal modulation symbol value intended for asingle OFDM tone-symbol, and the signal being communicated in two ormore consecutive OFDM symbol transmission time intervals. In someembodiments, a regular access signal can be considered a wake-up signalif the base station receiving the signal is in a transmit standby modeof operation. In some embodiments, the same air link resources reservedfor access signals may be reserved and used for wake-up signals. In somesuch embodiments, the access signals may be distinct from the wake-upsignals.

FIG. 19 is a flowchart 1900 of an exemplary method of operating awireless terminal, e.g., mobile node, in accordance with the presentinvention. The exemplary method of operation including establishing auser data channel with a base station for uplink data transmissionstarts in step 1902. For example, a wireless terminal may have poweredon and initialized in step 1902 and desires to establish an uplinkcommunications link with a base station network attachment pointcorresponding to the cellular coverage area in which it is located. Asanother example, a wireless terminal may be currently registered with abase station in whose cell it is located, but may be in a WT sleepstate, and in step 1902 its starts to initiate operations to transitionto a WT active state. As another example, a wireless terminal may becurrently an active user with a different base station point of networkattachment, located adjacent to the new base station that it seeks toestablish a user data channel, and the wireless terminal enters aboundary region. Operation proceeds from start step 1902 to step 1904.

In step 1904, the wireless terminal determines if the base station towhich it seeks to establish a user data channel is in a reduced activitystate of operation. Step 1904 includes sub-step 1906 and sub-step 1908.In sub-step 1906, the wireless terminal receives synchronization signalsfrom the base station. Then, in sub-step 1908, the wireless terminalmakes the determination of the base station mode of operation based onthe received synchronization signals.

In some embodiments, sub-step 1908 includes sub-step 1910, where thewireless terminal evaluates signal power levels to determine a basestation mode of operation. In some embodiments, higher signal powerlevels of at least some types of synchronization signals are indicativeof a full on mode of base station operation, while lower signal powerlevels of the same type of synchronization signals are indicative of areduced synchronization signaling mode of operation, e.g., a basestation sleep mode of operation. In various embodiments, thesynchronization signals include at least two types of signals and therelative power of the two types of signals is indicative of a basestation mode of operation. In some such embodiments, the at least twotypes of signals includes a first type of signal which is an OFDM beaconsignal and a second type of signal which is a pilot tone signal, and thebeacon tone signal has a per tone power at least three times the pertone signal power of a pilot tone signal. In some such embodiments theOFDM beacon per tone transmission power level is the same in both thebase station sleep mode and the base station active mode; however thepilot signal per tone transmission power is reduced in the base stationsleep mode of operation with respect to the base station active mode ofoperation.

In some embodiments, sub-step 1908 includes sub-step 1912 in which thewireless terminal determines a rate at which a first type ofsynchronization signals are received and correlates the determined rateto a corresponding base station mode of operation. In some suchembodiments, the first type of synchronization signals are pilot tonesignals. In some such embodiments, the base station is determined to bein a reduced synchronization signaling mode of operation, e.g., a sleepmode of base station operation, when the determined rate is below apredetermined threshold.

Operation proceeds from step 1904 to step 1914. In step 1914, thewireless terminal operation proceeds along different paths dependingupon whether or not the base station is in a reduced activity state ofoperation. If the base station is in a reduced state of activity, e.g.,a sleep state of base station operation, then operation proceeds fromstep 1914 to step 1916; however, if the base station is not in a reducedstate of activity, e.g., the base station is in a full-on active mode ofbase station operation, then operation proceeds from step 1914 to step1926.

In step 1916, the wireless terminal transmits a signal used to triggerthe base station to transition to a more active synchronizationsignaling mode of operation, e.g., transmits a wake- up signal, anaccess request signal, a hand-off signal, or a state transition requestsignal.

In some embodiments, a signal used to trigger the base station totransition into a more active synchronization signaling mode ofoperation is a wake-up signal. In some such embodiments thecharacteristics of the wake-up signal are such to provide easy detectionby a base station in sleep mode. In some embodiments, the wake-up signalincludes less than 5 OFDM tones. In some such embodiments, the wake-upsignal uses a single OFDM tone. In various embodiments, the wake-upsignal is transmitted for a continuous period of time lasting more thanone OFDM symbol transmission time period. In various embodiments, thewake-up signal is transmitted such that the signal occupies greater thana single OFDM transmission time interval, e.g., 2 successive OFDM symboltransmission time intervals, and the wireless terminal need not beprecisely timing synchronized with respect to the base station, e.g.,timing synchronization error may be greater than an OFDM cyclic prefixbut is small enough such that the wake-up signal can be detected by thebase station, e.g., the wireless terminal is synchronized with the basestation to within an OFDM symbol transmission time interval. In someembodiments, a predetermined set of tones is used for the wake-upsignal. In some embodiments, the predetermined set of tones includes atmost one tone. In various embodiments, the wake-up signal is transmittedby the wireless terminal at a per tone power level that is higher thanthe average power level used by the wireless terminal to transmit userdata. In some such embodiments, the wake-up signal is transmitted by thewireless terminal at the highest per tone power level used by thewireless terminal. In some embodiments, the wake- up signal iscommunicated using one of the tones utilized for access requestsignaling.

In some embodiments, a signal used to trigger the base station totransition into a more active synchronization signaling mode ofoperation is an access request signal, and the wireless terminaloperates differently following transmission of the access request signalif the transmission of the access request signal was to a base stationin a reduced synchronization mode of signaling operation than if thetransmission was to a base station in a full-on mode of synchronizationsignaling operation. In such an embodiment, the base station implementsdifferent processes in response to the received access request signaldepending upon the base station's current mode of operation.

In some embodiments, wherein the wireless terminal is currentlyconnected as an active user via a wireless link to a current basestation located adjacent to the base station to which the wirelessterminal seeks to wake-up and establish a user data channel, a signalused to trigger the base station to transition into a more activesynchronization mode of operation is transmitted through the currentbase station as part of a handoff operation. For example, a wirelessterminal may be in a sector or cell boundary region and anticipateswitching base station points of network attachment, and thus transmitsuch a signal to its current point of network attachment, and the signalmay be forwarded, e.g., via the backhaul network to the base stationthat needs to be woke-up. In this manner, hand-off delays may beminimized.

In some embodiments, wherein the wireless terminal is already registeredwith the base station that the wireless terminal seeks to cause totransition to a more active mode of synchronization signaling and thewireless terminal is in a wireless terminal sleep mode of operation inwhich the wireless terminal does not transmit user data, the signal usedto trigger the base station to transition into a more activesynchronization mode of operation is a state transition request signal,e.g., a request by the wireless terminal to transition from a WT sleepmode to a WT active mode.

Operation proceeds from step 1916 to step 1918. In step 1918, thewireless terminal waits a period of time for the base station totransition to an ON state. In some embodiments, the wireless terminalmonitors for a change in base station signaling, e.g., in terms of rateand/or power level of base station signaling to confirm that the basestation has transitioned into the active state of operation. In someembodiments, the wireless terminal repeats the signal intended to causethe transition if a base station mode transition is not observed withina predetermined amount of time, e.g., within a number of OFDM symboltransmission time intervals, or at an expected point within the timingstructure, e.g., the start of the next slot in the downlink timingstructure after allowing for signaling transmission times and basestation mode transitioning operations.

Then, in step 1920, the wireless terminal transmits registration and/oraccess request signals to the base station, e.g., an access requestsignals using a contention based access segment in an uplink timing andfrequency structure associated with the base station. For example, for awireless terminal new to the cell, a complete sequence of registrationand access request signaling may occur. However, for a wireless terminalcurrently registered with the base station, but in WT sleep mode, the WTmay have a registered user identifier but may seek to acquire an activeuser identifier and may initiate closed loop timing synchronization.

Operation proceeds from step 1920 to step 1922, where the wirelessterminal performs closed loop timing control based on feedback signalsfrom the base station. In some embodiments, wherein the wirelessterminal is being handed-off between two base station network attachmentpoints corresponding to the same cell, e.g., two sector attachmentpoints of the same base station or two carrier frequency attachmentpoints corresponding to the same sector of the same base station, someor all of the timing synchronization operations may be omitted. In someembodiments, closed loop power control pertaining to the wirelessterminal transmission power level is also performed.

Then, in step 1924, the wireless terminal initiates the transmission ofuser data to the base station. For example, the wireless terminal mayhave been previously assigned a base station active user identifier,e.g., in step 1920, the base station scheduler may have assigned one ormore uplink traffic channel segments to the wireless terminal, and thewireless terminal transmits user data using the assigned uplink trafficchannel segments.

Returning to step 1926, in step 1926, the wireless terminal initiatesregistration and/or access operations, and then in step 1928, thewireless terminal performs closed loop timing control based on feedbacksignals from the base station. Operation proceeds from step 1928 to step1930. In step 1930, the wireless terminal initiates the transmission ofuser data to the base station.

While described in the context of an OFDM system, many of the methodsand apparatus of the present invention, are applicable to a wide rangeof communications systems including many non-OFDM and/or non-cellularsystems.

In various embodiments nodes described herein are implemented using oneor more modules to perform the steps corresponding to one or moremethods of the present invention, for example, transitioning between twobase station modes of operation, operating in an active base stationmode of operation, operating in a transmit standby base station mode ofoperation, determining a base station mode of operation, signaling tocause a mode transition, processing mode transition related signaling,deciding whether or not to implement a mode transition, etc. In someembodiments various features of the present invention are implementedusing modules. Such modules may be implemented using software, hardwareor a combination of software and hardware. Many of the above describedmethods or method steps can be implemented using machine executableinstructions, such as software, included in a machine readable mediumsuch as a memory device, e.g., RAM, floppy disk, etc. to control amachine, e.g., general purpose computer with or without additionalhardware, to implement all or portions of the above described methods,e.g., in one or more nodes. Accordingly, among other things, the presentinvention is directed to a machine-readable medium including machineexecutable instructions for causing a machine, e.g., processor andassociated hardware, to perform one or more of the steps of theabove-described method(s).

Numerous additional variations on the methods and apparatus of thepresent invention described above will be apparent to those skilled inthe art in view of the above description of the invention. Suchvariations are to be considered within the scope of the invention. Themethods and apparatus of the present invention may be, and in variousembodiments are, used with CDMA, orthogonal frequency divisionmultiplexing (OFDM), and/or various other types of communicationstechniques which may be used to provide wireless communications linksbetween access nodes and mobile nodes. In some embodiments the accessnodes are implemented as base stations which establish communicationslinks with mobile nodes using OFDM and/or CDMA. In various embodimentsthe mobile nodes are implemented as notebook computers, personal dataassistants (PDAs), or other portable devices includingreceiver/transmitter circuits and logic and/or routines, forimplementing the methods of the present invention.

1. A method of operating a wireless terminal, the method comprising:determining if the base station to which the wireless terminal isseeking to establish a user data channel is in a reduced synchronizationsignaling mode of operation; and when said wireless terminal determinesthat said base station is in a reduced synchronization signaling mode ofoperation, transmitting a signal used to trigger the base station totransition into a more active synchronization signaling mode ofoperation.
 2. The method of claim 1, wherein said determining includes:receiving synchronization signals from said base station; and makingsaid determination based on the received synchronization signals.
 3. Themethod of claim 2, wherein said making of said determination based onthe received synchronization signals includes evaluating signal powerlevels to determine a base station mode of operation.
 4. The method ofclaim 3, wherein higher signal power levels are indicative of a full onmode of base station operation than lower signal power levels which areindicative of a reduced synchronization signaling mode of operation. 5.The method of claim 4, wherein said synchronization signals include atleast two types of signals and wherein the relative power of the twotypes of signals is indicative of the base station mode of operation. 6.The method of claim 5, wherein said at least two types of signalsincludes a first type of signal which is an OFDM beacon signal and asecond type of signal which is a pilot tone signal; and wherein saidbeacon signal has a per tone power at least three times the per tonesignal power of said pilot tone signal.
 7. The method of claim 2,wherein making said determination based on the received synchronizationsignals includes: determining a rate at which a first type ofsynchronization signals are received.
 8. The method of claim 7, whereinthe first type of synchronization signals are pilot tone signals.
 9. Themethod of claim 7, wherein said base station is determined to be in areduced synchronization signaling mode of operation when said determinedrate is below a predetermined threshold.
 10. The method of claim 2,wherein said signal used to trigger the base station to transition intoa more active synchronization signaling mode of operation is a wakeupsignal.
 11. The method of claim 10, wherein said wakeup signal includesless than 5 OFDM tones.
 12. The method of claim 11, wherein said wakeupsignal is transmitted for a continuous period of time lasting more thanone OFDM symbol transmission time period.
 13. The method of claim 12,wherein a predetermined set of tones is used for said wakeup signal. 14.The method of claim 13, wherein said predetermined set of tones includesat most one tone.
 15. The method of claim 2, wherein said signal used totrigger the base station to transition into a more activesynchronization signaling mode of operation is a wakeup signal which istransmitted by said wireless terminal at a per tone power level that ishigher than the average per tone power level used by the wirelessterminal to transmit user data.
 16. The method of claim 15, wherein saidwakeup signal is transmitted at the highest per tone power level used bysaid wireless terminal.
 17. The method of claim 2, wherein said signalused to trigger the base station to transition into a more activesynchronization signaling mode of operation is an access request signal,and wherein said wireless terminal operates differently followingtransmission of the access request signal if the transmission was to abase station in a reduced synchronization mode of signaling operationthan if the transmission was to a base station in a full-on mode ofsynchronization signaling operation.
 18. The method of claim 1, whereinsaid wireless terminal is connected by a wireless link to a current basestation located adjacent to said base station; and wherein transmittinga signal used to trigger the base station to transition into a moreactive synchronization signaling mode of operation is transmittedthrough said current base station as part of a handoff operation. 19.The method of claim 2, wherein said wireless terminal is alreadyregistered with said base station and said wireless terminal is in asleep mode of operation in which said wireless terminal does nottransmit user data; and wherein said signal used to trigger the basestation to transition into a more active synchronization signaling modeof operation is a state transition request signal.
 20. A wirelessterminal for communicating with a base station which supports a reducedsynchronization signaling mode of operation and a full onsynchronization mode of operation, the wireless terminal comprising: atransmitter; a base station mode determination module for determining ifsaid base station is operating in said reduce synchronization signalingmode of operation; and a wakeup signal module coupled responsive to saidbase station mode determination module for controlling said transmitterto transmit a signal used to trigger the base station to transition intoa more active synchronization signaling mode of operation.
 21. Thewireless terminal of claim 20, further comprising: a receiver forreceiving synchronization signals from said base station; and whereinsaid base station mode determination module processes receivedsynchronization signals to evaluate at least one of i) synchronizationsignal power levels and ii) a rate of at least some synchronizationsignals.
 22. The wireless terminal of claim 21, wherein said basestation mode determination module includes: a relative power leveldetermination module for determining the relative power levels of atleast two different type of received synchronization signals.
 23. Thewireless terminal of claim 21, wherein said at least two different typesof received synchronization signals are pilot tone signals and OFDMbeacon signals.
 24. The wireless terminal of claim 21, wherein said basestation mode determination module further includes a base station modedecision module for determining the mode of base station operation basedon the relative power level of at least two different synchronizationsignals.
 25. The wireless terminal of claim 21, wherein said basestation mode determination module determines the mode of base stationoperation based on the rate of at least one type of synchronizationsignal; and wherein said base station mode determination module includesa rate analysis module for distinguishing between receivedsynchronization signal rates corresponding to different modes of basestation operation.
 26. The wireless terminal of claim 25, wherein saidsynchronization signals are pilot tone signals.